A quote I will always remember from Dr. Deborah Forrester goes something like this: "The difference between a consultant and a resident is that when the resident is looking at the shoulder, the consultant is looking at the ribs." 

After recognizing the absent posterior 4th rib on the shoulder x-ray, the patient's clinical notes were examined and there was documentation of a previous heart surgery when the patient was an infant. In this case, they removed the posterior 4th rib to gain access through the chest wall for the procedure, but left the periosteum intact. This is why there are wispy osseous elements trailing from the remnants of this rib.

This finding should not be mistaken for an aggressive pathology in the context of previous thoracic surgery in the region, which should be sought out in the patient's history to clarify the finding before hunting for a nonexistent pathology.